There has heretofore been known a coordinate measuring instrument, wherein a measuring instrument is moved relative to a work to be measured, which is mounted on a mount plate, and a configuration and the like of the work are measured from relative displacement values of this measuring element. The coordinate measuring instruments of the type described are widely used in various fields of industries for displaying the advantages in raising the measuring accuracy, improving the operating efficiency of measurement and the like.
FIG. 1 shows a conventional coordinate measuring instrument. This coordinate measuring instrument is a tridimensional measuring instrument of the type, wherein a mount plate is fixed and the measuring element is movable. A gate-shaped measuring element support member 103 constituting a moving mechanism is mounted on a mount plate 102 rested on a base 100. This measuring element support member 103 comprises: a right and a left supports 104 and 105; a transverse member 106 transversely racked across top portions of these supports 104 and 105 in a direction of X-axis; a slider 107 provided in a manner to be movable along the transverse member 106; and a spindle 108 provided in a manner to be movable in a direction perpendicular to the slider 107, i.e. a direction of Z-axis. A measuring element 109 is secured to the bottom end of this spindle 108.
Movement of the measuring element 109 in a direction of Y-axis is performed due to the movement of the measuring element support member 103 along a guide rail member 110 affixed to the top surface of the mount plate 102, movement of the measuring element 109 in the direction of X-axis is performed due to the movement of the slider 107 along the transverse member 106, and further, movement of the measuring element 109 in the direction of Z-axis is performed due to the movement of the spindle 108 in the vertical direction. The guide rail member 110 is secured thereto with a detector 111 for the direction of Y-axis. A displacement value in the direction of Y-axis of the measuring element 109 due to the movement of the measuring element support member 103 along the guide rail member 110 is detected by this detector 111, a displacement value in the direction of X-axis of the measuring element 109 due to the movement of the slider 107 is detected by a detector 112 secured to the transverse member 106, and further, a displacement value in the direction of Z-axis of the measuring element 109 due to the vertical movement of the spindle 108 is detected by a detector 113 secured to the slider 107. The work to be measured is rested on and affixed to the top surface of the mount plate 102, whereby the measuring element 109 is brought into contact with the surface of the work and moved tridimensionally, so that the configuration and the like of the work can be measured.
In the conventional technique shown in FIG. 1, since the guide rail member 110 as being the reference of guide in the direction of Y-axis is secured to the top surface of the mount plate 102, troublesome assembling and adjusting works for securing the mounting accuracy of the guide rail member 110 are required, and the effective area of the top surface of the mount plate 102 is restricted by the guide rail, member 110, whereby the size of the work to be rested on the mount plate 102 is restricted. There have been such disadvantages that, since the guide rail member 110 becomes an obstacle to the work, when the work is carried onto the mount plate, only after the direction of the work is changed, the work can be mounted on the top surface of the mount plate 102, and that the height of the measuring element support member 103 is increased due to the height of the guide rail member 110, so that the height of the tridimensional measuring instrument is increased generally.
In addition to the above, it is difficult to operate the tridimensional measuring instrument from the side where the guide rail member 110 is provided, whereby the operating position is restricted. When the detector 111 is secured to the guide rail member 110 as shown in FIG. 1, there is a possibility that this detector 111 is contaminated or damaged during the operation of mounting the work onto the mount plate 102, thus presenting the disadvantage about the safety of the detector 111. The gate-shaped measuring element support member 103 is merely rested on the mount plate 102, whereby, when an external force acts sideways on the measuring element support member 103, there has a possibility that the element measuring support member 103 turns over.
According to the above-described conventional technique, when a left leg 103A and a right leg 103B of the measuring element support member 103 are provided with air bearings, respectively, so as to move the measuring element support member 103 relative to the mount plate 102, if the slider 107 is moved along the transverse member 106 and this movement is stopped at a position close to either the left support 104 or the right support 105, then the measuring element support member 103 is inclined and rotated about an axis parallel to the direction of Y-axis due to the fluctuations in the position of the center of gravity of the measuring element support member 103, whereby the measuring element 109 is varied in posture and an error occurs in a measured result of the work. When it is tried to obviate the disadvantages described above by the raise of air pressure, the measuring element support member 103 is increased in its floating value from the mounting plate 102, whereby the measuring element support member 103 becomes unstable, thus unabling to obviate the disadvantages.
The present invention has been developed to obviate the above-described disadvantages of the prior art, and is based on that, since the top surface of the mount plate is finished to be smooth and horizontal for resting thereon the work in particular, it is relatively easy that other surfaces are finished with high accuracy, securing the perpendicularity thereof with the top surface.
The present invention has as its object the provision of a coordinate measuring instrument, wherein, the mount plate itself is formed to provide the guide reference surface for the movement of the measuring element support member, whereby the provision of the guide rail member on the mount plate is dispensed with, so that the workabilities in assembling, adjustment and the like are improved, the effective area of the top surface of the mount plate is enlarged, the operation of mounting the work is facilitated and the controllability and the like of the measuring instrument are bettered. Moreover, the legs of the moving mechanism holding the measuring element as the measuring element support member are provided with air bearings opposed to vertical surfaces formed on the mount plate, whereby resistance against an external force in the traverse direction is generated in the measuring element support member, so that a possibility that the measuring element support member turns over can be eliminated.